The proposed research program is an extension of our long-term interest in the influence of physiological and experiential factors that impinge upon the developing organism and the consequences of these manipulations on the animal's later ability to interact with its environment. The activity of the pituitary-adrenal system continues to be a major dependent variable in many of our studies. We are proposing a set of experiments which will continue our examination of the influence of perinatal malnutrition on behavioral and physiological development in rodents. The dependent variables proposed in these studies will investigate the ability of the previously malnourished rat to respond to varying degrees of low-level stimulation and food-related tasks. In addition, a series of experiments are proposed which will investigate the psychobiology of attachment. In particular we are concerned with (a) the behavioral and physiological effects of prolonged separation in squirrel monkey mother and infants; (b) whether maternal behavior from another adult conspecific ("aunt") can assume some of the functions of the attachment figure (mother); and (c) whether the response to separation can be altered if the mother and/or infant are provided with predictability or control during repeated separations. The specificity of the behavioral and physiological responses to maternal figures will also be studied in the rhesus macaque. Other studies using rhesus macaques will investigate the response to different separation procedures and the effects of separation as a function of developmental changes in mother-infant relationships. We also propose to evaluate the pituitary-adrenal response of adult and juvenile conspecifics to stimuli produced by a separated infant and the development of fear of strangers in infant squirrel monkeys. Finally, we propose to establish a laboratory model of adolescence by examining behavioral and gonadal hormone changes that occur during puberty in the squirrel monkey.